text: TFH participates in nucleotide excision repair (NER) by opening the DNA double helix after damage is initially recognized.  NER is a multi-step pathway that removes a wide range of different damages that distort normal base pairing, including bulky chemical damages and UV-induced damages.  Individuals with mutational defects in genes specifying protein components that catalyze the NER pathway, including the TFH components, often display features of premature aging (see DNA damage theory of aging).